During early development and maturation, changes occur in the degree and type of adrenergic control influencing renal and systemic vascular resistance. Although circulating catecholamine levels are similar in the young and adult, the neonatal renal vasculature is more sensitive than the adult renal vasculature to the vasoconstrictor effects of epinephrine while the converse occurs in systemic blood vessels. Preliminary experiments from our laboratory have provided evidence suggesting that these varying neurotransmitter effects are due in part to age related changes in adrenergic receptor number and affinity. It is proposed to characterize alpha and beta adrenergic and dopaminergic receptors in cardiac, renal and systemic vessels in maturing puppies. Receptors will be studied in vitro using radioligands according to the methods of Lefkowitz. Adrenergic receptors in the kidney will be evaluated in vivo by examining the changes in renal blood flow, glomerular filtration rate and fractional sodium and potassium excretion induced by varying concentrations of alpha, beta and dopamine agonists and antagonists. These studies will be done in adults and puppies. An additional group of puppies will be studied during administration of a protein supplemented diet which has been shown to accelerate the maturational changes in the kidney. Isolated hind limb perfusion studied will provide in vivo data regarding systemic arterial receptors. These experiments may lead to a better understanding of the role of adrenergic receptors in the changes in regional vascular resistance associated with maturation.